The poem doesn't unfold in a specific location; it doesn't take place in a forest, or a hospital, or on the moon (though we do think that there should be more moon poems, if anyone's asking). Instead, "the mother" unfolds in the space of the speaker's mind. It's all about her thoughts, her emotions, her fantasies.
But it's also important to remember when the poem was written: 1945 This was almost thirty years before Roe v. Wade, the Supreme Court case that guaranteed abortion rights for women across America. Abortion was then, as it still is today, a controversial issue.
And, upon reading this poem, there's good reason why it's so controversial. It's an extraordinarily complex issue. The setting takes us inside the mother's mind, which is filled with doubt, guilt, love, fantasy—the works. But one thing that's utterly lacking here is any clear degree of certainty. We're in a setting of turmoil because that's what the speaker is experiencing to such an intense degree. Sheesh—no wonder the controversy persists.